test(12.1): verify live cloud browse integration

Phase 12.1 close — docs, version, and security evidence:
- Bump version 0.2.5 → 0.2.6 in backend/main.py, frontend/package.json
- CLAUDE.md: update current state to Phase 12.1 complete v0.2.6
- README.md: add Phase 12.1 corrections, live smoke variable names, Phase 13/14 exclusions
- RUNBOOK.md: add live smoke invocation, warning semantics table, fixture reconciliation procedure
- SECURITY.md: add Phase 12.1 Plan 04 threat table (T-12.1-16..20, T-12.1-SC) and gate evidence
- 12.1-VALIDATION.md: mark Plan 04 complete with final gate evidence

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "document-scanner-frontend",
-  "version": "0.2.5",
+  "version": "0.2.6",
   "type": "module",
   "scripts": {
     "dev": "vite",